These paintings were done with oil on paper using a "Dry Brush" technique. Oil dry brush is a painting technique where a paint brush is relatively dry but still holds paint. A very thin layer of color is applied to a paper.
Dry brush is layered layer after layer and reworked with an eraser, at this point it is possible to incorporate different lighting effects and details. Images painted with a dry brush appear very similar to a photo.
It is not an easy technique which requires a lot of time to learn and master.